Robert Downey Sr, a renowned filmmaker, has passed away at the age of 85, his son Robert Downey Jr has announced.

Writing on Instagram, the Iron Man actor wrote: “Last night, dad passed peacefully in his sleep after years of enduring the ravages of Parkinson’s.

“He was a true maverick filmmaker, and remained remarkably optimistic throughout. According to my stepmom’s calculations, they were happily married for just over 2000 years.

“Rosemary Rogers-Downey, you are a saint, and our thoughts and prayers are with you.”

Born in 1936 in New York City as Robert Elias Jr, he changed his name to Downey so he could enlist in the army.

After he left the military, Downey Sr made his name as a radical and anti-establishment filmmaker, and is known for projects such as Putney Swope and Greaser’s Palace.

Not only did he make films, he also starred in a number of them, including a turn in Boogie Nights as the studio manager and the show director in Magnolia.

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He directed his last film in 2005 – the documentary Rittenhouse Square – about the park of the same name in Philadelphia.

Downey Sr is survived by his wife, author Rosemary Rogers.